Light beam condensing apparatus and method of driving optical recording medium by applying the apparatus

ABSTRACT

A light beam condensing apparatus is provided to introduce a condensing spot of a laser beam onto an optical recording medium such as optical disks, and a method of driving the optical recording medium by applying the apparatus is disclosed. 
     There is provided modulation means  111  provided between a collimate lens  102  and an objective lens  105 , for externally controlling and varying an amplitude or a phase of a collimate beam  104 . The modulation means  111  is mechanically or electrically driven. Further, the modulation means  111  can be switched according to an operation mode of a drive unit or a kind of a recording medium  106  so as to provide a desired condensing spot shape.

This application is a divisional of application Ser. No. 08/395,922,filed Feb. 28, 1995, entitled LIGHT BEAM CONDENSING APPARATUS AND METHODOF DRIVING OPTICAL RECORDING MEDIUM BY APPYING THE APPAREATUS, and nowU.S. Pat. No. 5,974,011 which is a division of Ser. No. 08/185,457 filedJan. 24, 1994 and now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light beam condensing apparatus tointroduce a condensing spot of a laser beam onto an optical recordingmedium such as optical disks, and to a method of driving the opticalrecording medium by applying the apparatus.

2. Description of the Prior Art

There has been frequently studied a technique to improve recordingdensity of an optical disk so as to provide a large capacity opticaldisk. Thus, it has been known that reduction of a condensing spotdiameter of a laser light beam for recording and regeneration is veryeffective in the improvement of the recording density, and mean surfacerecording density substantially increases while being inverselyproportional to the square of the condensing spot diameter d_(SPOT). Thecondensing spot diameter d_(SPOT) is proportional to a wavelength λ of alaser to be used, and is inversely proportional to numerical aperture NAof an objective lens serving as a condenser, as shown in the followingexpression (1):

d_(SPOT)=k·(λ/NA)   (1)

where the proportional constant k is defined by a wave frontdistribution of light wave incident on the lens. According to theexpression (1), there are available three ways to reduce the condensingspot diameter d_(SPOT), i.e., the first way of reducing the wavelengthof the laser to be used, the second way of increasing the numericalaperture of the objective lens serving as the condenser, and the thirdway of using super resolution in a condensing optical system.

A description will now be given of a method for providing a smallcondensing spot diameter by utilizing the super resolution in thecondensing optical system. This method has been often disclosed inarticles such as 1) Yamanaka et al., “High Density Recording in OpticalDisk by Super Resolution” in Optics, Vol.18, No.12, (1989), or 2) H.Ando, “Phase-Shifting Apodizer of Three or More Portions” in JapaneseJournal of Applied Physics, Vol.31, (1992). In these methods disclosedin the articles, it is possible to reduce the condensing spot diameteron the basis of the same principle, as shown in FIGS. 1 and 2.

FIG. 1 shows a configuration of an optical system of a conventionalsuper resolution optical head as an example. In FIG. 1, referencenumeral 101 means a laser oscillator, 102 means a collimate lens, 103 isa beam forming prism, 105 is an objective lens, 106 is a recordingmedium, and 107 is a shading plate.

A description will now be given of the operation. Laser light from thelaser oscillator 101 serving as a light source is collimated through thecollimate lens 102 and the beam forming prism 103, resulting in parallellight. A laser beam 104 serving as the parallel light is focused andcondensed by the objective lens 105 on a recording surface of therecording medium 106. Here, the shading plate 107 is disposed across thelaser beam 104 so as to partially shade the laser beam 104. At the time,the condensing spot diameter d_(SPOT) of the laser beam 104 is variedaccording to a position and a shape of the shading plate 107, that is, awidth and a length thereof.

A description will now be given of the principle in the reduction of thecondensing spot diameter by the super resolution with reference to FIG.2. As shown in FIG. 2, in case the shading plate 107 is longer than abeam diameter D of the collimate beam 104, a condensing spot diameterd_(SPOT)t in a cross direction of the shading plate is defined as aratio of the beam diameter D to the width ΔW of the shading plate 107 ifthe width of the shading plate 107 is defined as ΔW. Further, acondensing spot diameter d_(SPOT)r in a longitudinal direction of theshading plate 107 is substantially irrelevant to the width ΔW. Here, asthe width ΔW becomes larger, sidelobes 108 in a condensing spot becomeshigher while the condensing spot diameter d_(SPOT)t of a mainlobe 109becomes smaller.

FIG. 3 shows a relation between ΔW/D and the condensing spot d_(SPOT)t.As understood from FIG. 3, as ΔW/D is more increased, the condensingspot diameter d_(SPOT)t is more reduced, and concurrently intensity ofthe sidelobe is more increased. Since increase of the sidelobe causes anincrease of crosstalk, it is impossible to allow the sidelobe to becomeso large. Here, ΔW/D=0 if the shading plate 107 is not employed. At thetime, if the condensing spot diameter is set to d_(SPOT)0, it ispossible to reduce the condensing spot diameter d_(SPOT)t to 10% degreeas compared with d_(SPOT)0 when the sidelobe intensity can be in a rangeof 0.1 times the mainlobe or less. In such a way, it is possible toreduce the condensing spot diameter with the constant laser wavelength λand the constant numerical aperture NA of the lens by shading a vicinityof an intermediate portion of the collimate beam in a super-resolutionoptical head. When the shading plate 107 is coplanarly rotated by 90°,the condensing spot diameter d_(SPOT)t is left as it is d_(SPOT)0, andthe condensing spot diameter d_(SPOT)r is reduced.

As set forth above, the principle of the super resolution utilizes thecharacter of focusing light wave that it is possible to vary theintensity distribution at the condensing spot by modulating a wave frontof the collimate beam 104 on an entrance surface of the objective lens105. That is, the shading plate 107 shown in FIG. 2 corresponds to spacemodulation which is performed so as to set an amplitude distribution ofthe collimate beam 104 on the entrance surface of the objective lens 105to zero in the vicinity of the intermediate portion of the collimatebeam 104. Accordingly, laser power at a shaded portion is lost.

Further, on the basis of the principle of the super resolution, it isalso possible to vary the intensity distribution of the condensing spotby modulating a phase distribution of the collimate beam 104 on theentrance surface of the objective lens 105. That is, it is possible toform a condensing spot shape by providing appropriate phase shiftaccording to a position on the entrance surface of the objective lens105. This method is employed in the article 2) as described before. Inthis case, the collimate beam 104 is not shaded so that there is nopartial loss of the laser power due to the shading.

Alternatively, in another known technique, a distribution is caused inindexes of refraction in order to provide phase modulation totransmitted light. Assumed that there is difference Δn between theindexes of refraction sensed by the transmitted light at two portions ofa modulation plate when light having the wavelength λ passes through themodulation plate having a thickness of L. Consequently, in the lightbeam passing through both the portions, there is generated a phasedifference Δφ expressed by the following expression (2):

Δφ=2π(L/λ)·Δn   (2)

A phase of the transmitted light is modulated by the phase difference.It must be noted that a method of the phase modulation of thetransmitted light should not be limited to a method to provide adifference in an optical path length by the difference in the indexes ofrefraction. It is similarly possible to provide the difference in theoptical path length by varying the thickness of the modulation plate soas to perform the phase modulation of the transmitted light.

The recording density of the optical disk can be expressed by theproduct of recording density in a direction parallel to a recordingtrack (i.e., track recording density BPI) and recording density in adirection perpendicular to the recording track (i.e., track densityTPI). Therefore, it is possible to improve surface recording density ofthe optical disk by improving the BPI and the TPI, respectively. Theconventional embodiment shown in FIG. 2 is provided to improve the BPI.For example, if a concentrically circular shading plate to shade theintermediate portion exclusively is employed instead of the shadingplate 107 shown in FIG. 2, the condensing spot has a concentricallycircular shape so that the mainlobe 109 is surrounded by the sidelobe108. In this case, the condensing spot diameter of the mainlobe 109 canbe reduced. Thus, it is possible to concurrently improve the BPI and theTPI by using the condensing spot.

As set forth above, the reduction of the condensing spot diameter by thesuper resolution is an effective technique to improve the recordingdensity. According to the prior art, it is possible to provide aconstant condensing spot diameter by varying the amplitude or the phaseof the transmitted light by a fixed optical component such as theshading plate, or the phase plate. However, in the prior art, it isimpossible to vary a parameter of the super resolution, that is, themodulation amount applied to the wave front of the collimate beam on theentrance surface of the objective lens during the operation in onecondensing apparatus so as to dynamically vary the condensing spotdiameter or the condensing spot shape of an optical disk unit.

On the other hand, in the current market, there are employed the opticaldisks compatible to the optical disk standard which is standardized bythe ISO standard or the like. Most of these disks have a track pitch of1.6 (μm) and the track recording density of 25 (kbit/inch). Further, thelarge capacity optical disk has been developed in recent years, and thetrack pitch is more reduce and the track recording density is moreincreased if it is possible to provide the practical large capacityoptical disk having more improved recording density than that of theconventional optical disk. Accordingly, a condensing spot diametersmaller than that in the prior art is required for recording andregenerating information. The condensing spot diameter can be providedby applying a shorter wavelength laser, an objective lens having largernumerical aperture, or the super resolution as described before. In thiscase, it is to be understood that the condensing spot diameter isdesigned so as to be adaptable to the track pitch or the track recordingdensity of a newly developed large capacity optical disk.

Here, compatibility of an optical disk drive becomes a major issue. Thatis, in case the optical disk drive is provided with a function to driveboth the newly developed large capacity optical disk and the opticaldisks based upon the conventional standard, there are the followingthree problems. The first problem relates to a tracking servo. A servosensor signal for tracking is detected depending upon diffractionphenomena of the spot on the disk surface because of a guide groove,i.e., a periodic structure of a groove and a land on the optical disk.Hence, if the condensing spot is designed so as to be adaptable to anarrow-width track pitch, there is a drawback in that it is not possibleto sufficiently provide a servo error signal for tracking when theconventional optical disk having a wide-width track pitch is driven.

The second problem occurs at a time to read an emboss signal. Whileinformation of the emboss signal is recorded on the optical disk in aform of a phase bit, the signal regeneration is performed depending upona principle that condensed light is diffracted by the phase bit, and anamount of reflected light to be received by the detector is variedaccording to the presence or absence of the bit. Therefore, it isimpossible to provide a sufficient variation rate by the diffraction incase the condensing spot diameter is too small with respect to the phasebit. As a result, there is another drawback in that reading accuracy isreduced or incapability of reading occurs due to a reduced regenerativeamplitude of the emboss signal.

The third problem occurs when the information on the medium is erased ina rewritable optical disk. In optical disks which is recorded and erasedby thermal energy of the condensed light such as magneto-optical medium,or phase varying medium, when a signal recorded on a low density mediumhaving the wide-width track is erased by the condensing spot having asmall diameter, it is impossible to erase an entire width of therecorded mark since an erasable width is narrow, resulting in anunerased portion. As a result, there is still another drawback in thatthe unerased portion is left as the crosstalk, and increases occurrenceof regeneration error when the erasing and recording is repeated.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of the present invention toprovide a light beam condensing apparatus which can ensure compatibilityof many kinds of optical recording media as a main function required ina medium interchangeable information recording apparatus, and a methodof driving an optical recording medium by applying the light beamcondensing apparatus.

It is another object of the present invention to attempt improvement ofmain performances required in the optical disk drive, such asimprovement of data reliability and seek reliability, and extension of adisk receiving range by effectively using functions which can realizedaccording to the present invention.

According to the first aspect of the present invention, for achievingthe above-mentioned objects, there is provided a light beam condensingapparatus including an objective lens to condense a collimate beam so asto introduce a condensing spot of the collimate beam onto an opticalrecording medium, and modulation means for varying a shape of thecondensing spot by modulating the collimate beam.

As stated above, in the light beam condensing apparatus according to thefirst aspect of the present invention, a laser beam emitted from a laseroscillator is transformed into the collimate beam by a collimate lens.The objective lens condenses the collimate beam to introduce thecondensing spot of the collimate beam onto the optical recording medium.Further, the modulation means varies the shape of the condensing spot bymodulating the collimate beam. Therefore, it is possible to use asmall-diameter condensing spot with respect to a high recording densitymedium, and use a large-diameter condensing spot with respect to a lowrecording density medium.

According to the second aspect of the present invention, there isprovided a light beam condensing apparatus including modulation meansfor varying a shape of a condensing spot by modulating a collimate beam,and control means for controlling the modulation means to vary the shapeof the condensing spot.

As stated above, in the light beam condensing apparatus according to thesecond aspect of the present invention, since the control means isprovided to control the modulation means, it is possible to control themodulation means.

According to the third aspect of the present invention, there isprovided a light beam condensing apparatus to vary transmission factorof a collimate beam by modulation means so as to vary a shape of acondensing spot.

As stated above, in the light beam condensing apparatus according to thethird aspect of the present invention, it is possible to vary thetransmission factor of the collimate beam by the modulation means so asto vary the shape of the condensing spot. As a result, it is possible toadjust a diameter of the condensing spot according to high or lowrecording density of an optical recording medium.

According to the fourth aspect of the present invention, there isprovided a light beam condensing apparatus to vary a phase of acollimate beam by modulation means so as to vary a shape of a condensingspot.

As stated above, in the light beam condensing apparatus according to thefourth aspect of the present invention, it is possible to vary the phaseof the collimate beam by the modulation means so as to vary the shape ofthe condensing spot. Therefore, it is possible to reduce or extend adiameter of the condensing spot without shading the collimate beam.

According to the fifth aspect of the present invention, there isprovided a light beam condensing apparatus to modulate a collimate beamso as to vary a shape of a condensing spot when a modulation plate ispositioned in a direction perpendicular to an optical axis of thecollimate beam, and to cease the modulation of the collimate beam whenmodulation means is positioned in a direction parallel to the opticalaxis of the collimate beam.

As stated above, in the light beam condensing apparatus according to thefifth aspect of the present invention, the modulation means is providedin a flat shape, and it is possible to modulate the collimate beam so asto vary the shape of the condensing spot when the modulation plate ispositioned in the direction perpendicular to the optical axis of thecollimate beam, and to cease the modulation of the collimate beam whenmodulation means is positioned in the direction parallel to the opticalaxis of the collimate beam. Therefore, the shape of the condensing spotcan be switched over by simply rotating the flat modulation means.

According to the sixth aspect of the present invention, there isprovided a light beam condensing apparatus in which modulation means isrotatably supported about an optical axis of a collimate beam when themodulation means is positioned in a direction perpendicular to theoptical axis of the collimate beam.

As stated above, in the light beam condensing apparatus according to thesixth aspect of the present invention, the flat modulation means can berotated about the optical axis of the collimate beam when the modulationmeans is positioned in the direction perpendicular to the optical axisof the collimate beam. Therefore, a shape of a condensing spot can beswitched over as in the fifth aspect, and the condensing spot can bereduced in all directions by rotating the modulation means about theoptical axis.

According to the seventh aspect of the present invention, there isprovided a light beam condensing apparatus in which, when any one ofmodulation plates is positioned in a direction perpendicular to anoptical axis of a collimate beam to vary a shape of a condensing spot,the other modulation plate is positioned in a direction parallel to theoptical axis of the collimate beam.

As stated above, the light beam condensing apparatus according to theseventh aspect of the present invention includes the pair of modulationplates which are mounted in a substantially cross form, and when any oneof the modulation plates is positioned in the direction perpendicular tothe optical axis of the collimate beam to vary the shape of thecondensing spot, the other modulation plate is positioned in thedirection parallel to the optical axis of the collimate beam. Therefore,two kinds of condensing spot diameters can be switched over from one toanother by positioning the one modulation plate and the other modulationplate in the direction perpendicular to the optical axis of thecollimate beam.

According to the eighth aspect of the present invention, there isprovided a light beam condensing apparatus including modulation means.The modulation means has a cylindrical body whose peripheral surface isprovided with a modulation pattern, and a shape of a condensing spot isvaried by positioning the modulation pattern of the peripheral surfaceacross a course of a collimate beam.

As stated above, the light beam condensing apparatus according to theeighth aspect of the present invention includes the cylindricalmodulation means whose peripheral surface is provided with themodulation pattern, and it is possible to vary the shape of thecondensing spot by positioning the modulation pattern of the peripheralsurface across the course of the collimate beam. Therefore, since aplurality of modulation patterns can be formed on the peripheral surfaceof the cylindrical body, it is possible to provide different types ofthe shapes of the condensing spot.

According to the ninth aspect of the present invention, there isprovided a light beam condensing apparatus in which modulation meansincludes a pair of modulation plates, and when the respective modulationplates are positioned in a direction perpendicular to an optical axis ofa collimate beam, the respective modulation plates are coplanarlypositioned, and a modulation pattern is provided by the respectivemodulation plates.

As stated above, in the light beam condensing apparatus according to theninth aspect of the present invention, the modulation means includes thepair of modulation plates, and when the respective modulation plates arepositioned in the direction perpendicular to the optical axis of thecollimate beam, the respective modulation plates are coplanarlypositioned, and the modulation pattern is provided by the respectivemodulation plates. Therefore, it is possible to optionally select amodulation mode to provide no modulation by positioning the respectivemodulation plates in a direction parallel to the optical axis of thecollimate beam, a first modulation mode to provide the collimate beamwith first modulation by positioning so as to pass the collimate beamthrough a half surface of one of the respective modulation plates, and asecond modulation mode to provide the collimate beam with secondmodulation by positioning so as to pass the collimate beam through ahalf surface of the other of the respective modulation plates.

According to the tenth aspect of the present invention, there isprovided a light beam condensing apparatus including modulation means.The modulation means has a modulation plate which is provided with aplurality of modulation patterns, and is supported slidably in adirection perpendicular to an optical axis of a collimate beam, and themodulation means can position a desired modulation pattern in theplurality of modulation patterns across an optical path of the collimatebeam.

As stated above, the light beam condensing apparatus according to thetenth aspect of the present invention includes the modulation means. Themodulation means has the modulation plate which is provided with theplurality of modulation patterns, and is supported slidably in thedirection perpendicular to the optical axis of the collimate beam, andthe modulation means can position the desired modulation pattern in theplurality of modulation patterns across the optical path of thecollimate beam. Therefore, it is possible to easily increase the numberof the modulation patterns.

According to the eleventh aspect of the present invention, there isprovided a light beam condensing apparatus including modulation means.The modulation means has a modulation plate which is formed by aplurality of optical components, and is disposed across an optical pathof a collimate beam, and the modulation means varies a modulationpattern of the modulation plate by applying voltage to the opticalcomponents.

As stated above, the light beam condensing apparatus according to theeleventh aspect of the present invention includes the modulation means.The modulation means has the modulation plate which is formed by theplurality of optical components, and is disposed across the optical pathof the collimate beam, and the modulation means can vary the modulationpattern of the modulation plate by applying the voltage to the opticalcomponents. Therefore, since the modulation pattern can be electricallyvaried, it is possible to accelerate a switching speed.

According to the twelfth aspect of the present invention, there isprovided a light beam condensing apparatus in which a modulation patternof modulation means is formed by a rectangular modulation sectionpositioned at an intermediate portion of a collimate beam, and having alongitudinal side longer than a collimate beam diameter, and by amodulation section positioned at the other portion of the collimatebeam.

As stated above, in the light beam condensing apparatus according to thetwelfth aspect of the present invention, the modulation pattern of themodulation means is formed by the rectangular modulation section whichis positioned at the intermediate portion of the collimate beam, and hasthe longitudinal side longer than the collimate beam diameter, and bythe modulation section positioned at the other portion of the collimatebeam. Therefore, it is possible to reduce or extend a diameter of acondensing spot in one direction by the modulation section at theintermediate portion.

According to the thirteenth aspect of the present invention, there isprovided a light beam condensing apparatus in which a modulation patternof modulation means is formed by a circular modulation sectionpositioned coaxially with a collimate beam, and having a diametersmaller than a collimate beam diameter, and by a modulation sectionpositioned at the other portion of the collimate beam.

As stated above, in the light beam condensing apparatus according to thethirteenth aspect of the present invention, the modulation pattern ofthe modulation means is formed by the circular modulation sectionpositioned coaxially with the collimate beam, and having the diametersmaller than the collimate beam diameter, and by the modulation sectionpositioned at the other portion of the collimate beam. Therefore, it ispossible to reduce or extend a diameter of a condensing spot by thecircular modulation section in all directions.

According to the fourteenth aspect of the present invention, there isprovided a method of driving an optical recording medium by applying alight beam condensing apparatus. The method comprises the steps ofsetting a condensing spot shape of a condensing beam focused into arecording bit area of an optical recording medium to be adaptable to atrack pitch, and performing recording and regeneration of the opticalrecording medium at the condensing spot having the set shape.

As stated above, in the method of driving the optical recording mediumby applying the light beam condensing apparatus according to thefourteenth aspect of the present invention, track pitch information inthe recording bit area is read by the condensing beam emitted from thelight beam condensing apparatus to control modulation means of the lightbeam condensing apparatus depending upon the read track pitchinformation so as to modulate a collimate beam, and the condensing spotshape of the condensing beam focused into the recording bit area of theoptical recording medium is set to be adaptable to the track pitch.Therefore, the condensing spot can be switched over according to thetrack pitch of the optical recording medium.

According to the fifteenth aspect of the present invention, there isprovided a method of driving an optical recording medium by applying alight beam condensing apparatus. The method comprises the steps ofdetecting an amplitude of a tracking servo sensor signal at a time of aset condensing spot shape, adjusting the set condensing spot shape bycontrolling modulation means so as to maximize the detected amplitude,and performing recording and regeneration of the optical recordingmedium at the adjusted condensing spot.

As stated above, in the method of driving the optical recording mediumby applying the light beam condensing apparatus according to thefifteenth aspect of the present invention, the amplitude of the trackingservo sensor signal at the time of set condensing spot shape isdetected, and the set condensing spot shape is adjusted by controllingthe modulation means so as to maximize the detected amplitude.Therefore, it is possible to absorb variation in the tracking servosignal which is different for each combination of the optical recordingmedium and a drive unit thereof.

According to the sixteenth aspect of the present invention, there isprovided a method of driving an optical recording medium by applying alight beam condensing apparatus. The method comprises the steps ofdetecting an amplitude of a regenerative signal of an emboss signalbefore performing regeneration of the optical recording medium with acondensing spot, and controlling modulation means to maximize thedetected amplitude so as to adjust a condensing spot shape to be optimalfor information regeneration.

As stated above, in the method of driving the optical recording mediumby applying the light beam condensing apparatus according to thesixteenth aspect of the present invention, it is possible to detect theamplitude of the regenerative signal of the emboss signal beforeperforming the regeneration of the optical recording medium with thecondensing spot, and control the modulation means to maximize thedetected amplitude so as to adjust the condensing spot shape to beoptimal for the information regeneration. Therefore, it is possible toabsorb variation in an information regenerating signal characteristicwhich is different for each combination of the optical recording mediumand a drive unit thereof.

According to the seventeenth aspect of the present invention, there isprovided a method of driving an optical recording medium by applying alight beam condensing apparatus. The method comprises the steps ofsetting a condensing spot shape to have a large diameter by controllingmodulation means of the light beam condensing apparatus before readingtrack pitch information in a recording bit area.

As stated above, in the method of driving the optical recording mediumby applying the light beam condensing apparatus according to theseventeenth aspect of the present invention, it is possible to set thecondensing spot shape to have the large diameter by controlling themodulation means of the light beam condensing apparatus before readingthe track pitch information in the recording bit area. Therefore, it ispossible to improve reading accuracy of the track pitch information inthe recording bit area with respect to various types of opticalrecording media.

According to the eighteenth aspect of the present invention, there isprovided a method of driving an optical recording medium by applying alight beam condensing apparatus. The method comprises the steps ofsetting a condensing spot shape in a large size by controllingmodulation means of the light beam condensing apparatus before focusingon a control track area for reading track pitch information.

As stated above, in the method of driving the optical recording mediumby applying the light beam condensing apparatus according to theeighteenth aspect of the present invention, it is possible to set thecondensing spot shape in the large size by controlling the modulationmeans of the light beam condensing apparatus before the focus pulling infor reading the track pitch information in the recording bit area.Therefore, it is possible to improve stability of the focus pulling in.

According to the nineteenth aspect of the present invention, there isprovided a method of driving an optical recording medium by applying alight beam condensing apparatus. The method comprises the steps ofcontrolling modulation means of the light beam condensing apparatusaccording to a driving condition of the recording medium to switch ashape of a condensing spot which is focused on the optical recordingmedium.

As stated above, in the method of driving the optical recording mediumby applying the light beam condensing apparatus according to thenineteenth aspect of the present invention, the light beam condensingapparatus is provided to emit a laser beam from a laser oscillator,transform the emitted laser beam into a collimate beam and condense thecollimate beam so as to introduce the beam into a bit area of theoptical recording medium. In the light beam condensing apparatus, it ispossible to control the modulation means of the light beam condensingapparatus according to the driving condition of the recording medium soas to switch the shape of the condensing spot which is focused on theoptical recording medium. Therefore, control can be made such that spotshape modification is provided at a time of seek and regeneration, andthe spot shape modification is not provided at a time of recording.

According to the twentieth aspect of the present invention, there isprovided a method of driving an optical recording medium by applying alight beam condensing apparatus. The method comprises the steps of, incase it is detected that sector read is not normal at a time ofregeneration of the optical recording medium, controlling modulationmeans depending upon the detected signal so as to adjust a condensingspot shape, retry the sector read, and repeat the above steps until thesector read can be normally performed.

As stated above, in the method of driving the optical recording mediumby applying the light beam condensing apparatus according to thetwentieth aspect of the present invention, it is possible to, in case itis detected that the sector read is not normal at the time ofregeneration of the optical recording medium, control the modulationmeans depending upon the detected signal so as to adjust the condensingspot shape, retry the sector read, and repeat the above steps until thesector read can be normally performed. Therefore, it is possible toimprove such a possibility that a condition incapable of reading asignal can be avoided.

The above and further objects and novel features of the invention willmore fully appear from the following detailed description when the sameis read in connection with the accompanying drawing. It is to beexpressly understood, however, that the drawings are for purpose ofillustration only and are not intended as a definition of the limits ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general view of a conventional super-resolution light beamcondensing apparatus;

FIG. 2 is an explanatory view illustrating a principle of reduction of acondensing spot diameter according to a conventional super resolution;

FIG. 3 is an explanatory view illustrating a relationship between aconventional shading plate width and the condensing spot diameter;

FIG. 4 is a general view of a condensing spot shape variable type oflight beam condensing apparatus according to the present invention;

FIG. 5 is a plan view of a transmission factor variable modulation plateaccording to the present invention;

FIG. 6 is a plan view of modulation means for modulating an amplitude ofthe transmitting light according to the present invention;

FIG. 7 is a plan view of modulation means for modulating a phase of thetransmitting light according to the present invention;

FIG. 8 is a plan view of a space modulation pattern of modulation meansaccording to the present invention;

FIG. 9 is a plan view of another space modulation pattern of themodulation means according to the present invention;

FIG. 10 is a plan view of still another space modulation pattern of themodulation means according to the present invention;

FIG. 11 is an explanatory view illustrating space amplitude modulationusing a rotary modulation plate according to the present invention;

FIG. 12 is a plan view of the rotary modulation plate according to thepresent invention;

FIG. 13 is a plan view of the rotary modulation plate according to thepresent invention;

FIG. 14 is a plan view, a top view, and a side view of a two-planerotary modulation plate;

FIG. 15 is an explanatory view illustrating space amplitude modulationusing a cylindrical rotary modulation plate according to the presentinvention;

FIG. 16 is a perspective view of a rectangular and cylindrical rotarymodulation plate according to the present invention;

FIG. 17 is a perspective view of a cylindrical rotary modulation plateaccording to the present invention;

FIG. 18 is a perspective view of a two-axis rotary modulation plateaccording to the present invention;

FIG. 19 is a perspective view of a pair of rotary modulation platesaccording to the present invention;

FIG. 20 is an explanatory view illustrating space amplitude modulationusing a translating modulation plate according to the present invention;

FIG. 21 is a plan view of a modulation plate for primary translationaccording to the present invention;

FIG. 22 is a plan view of a modulation plate for secondary translationaccording to the present invention;

FIG. 23 is an explanatory view illustrating conditions of phasemodulation by the modulation means according to the present invention;

FIG. 24 is an explanatory view illustrating space amplitude modulationusing a flat liquid crystal switch according to the present invention;

FIG. 25 is an explanatory view illustrating a method of controlling theflat liquid crystal switch according to the present invention;

FIG. 26 is an explanatory view illustrating space phase modulation usingthe flat phase modulator according to the present invention;

FIG. 27 is an explanatory view illustrating a method of controlling theflat phase modulator according to the present invention;

FIG. 28 is an explanatory view illustrating space phase modulation usinga bulk-like phase modulator according to the present invention;

FIG. 29 is a front view of the bulk-like phase modulator according tothe present invention;

FIG. 30 is a diagram showing the algorithm which illustrates acompatibility ensuring procedure with respect to various types of trackpitches according to the present invention;

FIG. 31 is an explanatory view illustrating a method of setting thecondensed spot diameter with respect to the track pitch according to thepresent invention;

FIG. 32 is a diagram showing the algorithm which illustrates acondensing spot size optimizing procedure for tracking according to thepresent invention;

FIG. 33 is a block diagram of an amplitude monitor circuit for atracking servo sensor signal according to the present invention;

FIG. 34 is a diagram showing the algorithm which illustrates acondensing spot size optimizing procedure for signal regenerationaccording to the present invention;

FIG. 35 is a block diagram of an amplitude monitor circuit for aregenerative signal according to the present invention;

FIG. 36 is an explanatory view illustrating control of each condensingspot shape for each operation of optical disk driving according to thepresent invention;

FIG. 37 is a diagram showing the algorithm which illustrates a method ofimproving retry processing ability for regeneration by adjusting thecondensing spot diameter according to the present invention;

FIG. 38 is a diagram showing the algorithm which illustrates a method ofimproving PEP reading ability by adjusting the condensing spot diameteraccording to the present invention;

FIG. 39 is an explanatory view illustrating a relation between thecondensing spot and recorded bits at a time of reading PEP in controltrack area; and

FIG. 40 is a diagram showing the algorithm which illustrates a focuspulling in stabilizing procedure by adjusting the condensing spotdiameter according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the invention will now be described in detailreferring to the accompanying drawings.

Embodiment 1

A description will now be given of one embodiment of the presentinvention. FIG. 4 is a general view of a light beam condensing apparatusaccording to one embodiment of the present invention. In FIG. 4,reference numeral 110 means control means, and 111 means modulationmeans. In FIG. 4, component parts identical with or equivalent to thoseof a conventional light beam condensing apparatus shown in FIG. 1 aredesignated by the same reference numerals, and descriptions thereof areomitted.

A description will now be given of the operation. A laser light from alaser oscillator 101 serving as a light source is collimated through acollimate lens 102 and a beam forming prism 103, resulting in parallellight. A collimate beam 104 serving as the parallel light is focused andcondensed upon a recording surface of a recording medium (opticalrecording medium) 106 through an objective lens 105. In this case, themodulation means 111 is mounted across the collimate beam 104 so thatthe modulation means 111 partially shades the collimate beam 104.

A description will now be given of the modulation means 111. FIG. 5shows an arrangement principle of the modulation means 111 according tothe embodiment 1. In FIG. 5, reference numeral 112 means an intermediateportion of a beam transmitting surface of the modulation means 111, and113 means a side portion thereof. In the arrangement, it is possible tocontrol transmission factor of the intermediate portion (i.e., amodulation portion positioned at the intermediate portion) 112 by anexternal signal. Next, the operation will be described hereinafter. Whenthe control means 110 is controlled so as to set the transmission factorof the intermediate portion 112 to zero, that is, provide a shadedcondition, as in a conventional shading plate 107 shown in FIG. 1, it ispossible to obtain a super-resolution spot having a diameter reduced inone direction. Further, when the control means 110 is controlled so asto set the transmission factor of the intermediate portion 112 to 1,that is, provide a transparent condition, it is possible to obtain anormal condensing spot without the super resolution.

It is thereby possible to drive a high recording density medium by usinga small-diameter condensing spot, and drive a low recording densitymedium by using the normal condensing spot. As a result, both aconventionally standardized medium and a large capacity medium can bedriven by the same optical head.

Embodiment 2

FIG. 6 shows an arrangement principle of modulation means 111 accordingto the embodiment 2. Though it is possible to control the transmissionfactor of the intermediate portion 112 exclusively in the embodiment 1,in the embodiment 2, it is possible to control the transmission factorof the intermediate portion 112, and the transmission factor of sideportions 113, 113 in response to a signal from control means 110. Thus,the embodiment 2 is different from the embodiment 1 in that it ispossible to obtain a condensing spot having a larger diameter in onedirection than that of a normal condensing spot by setting thetransmission factor of the intermediate portion 112 to 1, and settingthe transmission factor of the side portions 113, 113 to zero in theembodiment 2. When a low recording density medium is driven by anoptical head for driving a large capacity medium by using, for example,a shorter wavelength laser rather than super resolution, the modulationmeans 111 according to the embodiment 2 is effective in extending a spotin a radial direction of an optical disk to manage a wide-width trackpitch.

Embodiment 3

FIG. 7 shows an arrangement principle of modulation means 111 accordingto the embodiment 3. Though it is possible to control the transmissionfactor in the embodiment 2, in the embodiment 3, it is possible tocontrol index of refraction to transmitted light at an intermediateportion 112 of the modulation means 111, and index of refraction totransmitted light at side portions (a modulation portion positioned at aportion other than the intermediate portion 112) 113, 113 in response toa signal from control means 110. Thereby, while modulation is providedin the amplitude distribution of the transmitted light in the embodiment2, the modulation is provided in a phase distribution of the transmittedlight in the embodiment 3. In this regard, the embodiment 3 is differentfrom the embodiment 2. Therefore, in the embodiment 3, it is possible toreduce and extend a condensing spot diameter as in the embodiment 2, andprevent loss of power due to shading, which can not be prevented in theembodiment 2.

The embodiment 3 has been described with reference to a case where themodulation is provided in the phase distribution of the transmittedlight. However, it must be noted that the present invention should notbe limited to this case, and both the amplitude distribution and thephase distribution of the transmitted light may be concurrentlymodulated so as to provide a more appropriate condensing spot shade.

Embodiment 4

The embodiments 1 to 3 have been described with reference to a casewhere the modulation means 111 is divided into three sections. However,it must be noted that the present invention should not be limited to thedivision of the modulation means 111 into the three sections. Forexample, the modulation means 111 may be divided into two sections,i.e., a circular inner portion 141 concentric with a collimate beam 104and a ring type outer portion 142 as shown in FIG. 8 according to theembodiment 4. It is thereby possible to provide a super-resolution spothaving a diameter reduced in all directions, or a condensing spot havinga diameter extended in all directions by controlling light transmissionfactor and index of refraction of the inner portion 141 and the outerportion 142.

FIG. 9 shows the modulation means 111 which is divided by substantiallyX-shaped lines into four sections. In this case, when a control signalis provided to generate the same modulation amount at two components 143and 145 or 144 and 146 having vertically opposite angles, it is possibleto obtain the condensing spot having a diameter which is reduced in onedirection, and is extended in another direction perpendicular to thedirection.

Referring to FIG. 10, the embodiments in FIGS. 8 and 9 are combined. Inthe embodiment shown in FIG. 10, it is possible to combine controlmethods of the modulation means 111 which are respectively enabled inthe embodiments in FIGS. 8 and 9. Therefore, setting of a condensingspot shape can be flexibly varied by the methods as described in theembodiments in FIGS. 8 and 9. As a result, according to the embodimentshown in FIG. 10, it is possible to provide the optimal condition formedia having various types of track densities and recording densities.

Embodiment 5

The embodiments 1 to 4 have been described with reference to a casewhere a collimate beam 104 is modulated by controlling the lighttransmission factor and the index of refraction of the modulation means111. However, the collimate beam 104 may be modulated by mechanicallyrotating a modulation plate 211 of the modulation means 111 as shown inFIG. 11 according to the embodiment 5. The embodiment 5 will behereinafter described with reference to FIG. 11. The modulation plate211 is provided in a disk-like form as shown in FIG. 11, and themodulation plate 211 has a thickness which can be neglected with respectto a beam width. The modulation plate 211 is rotatably supported on anoptical axis of the collimate beam 104 through rotation axes 211 a, 211a. The rotation of the modulation plate 211 is controlled by controlmeans 110 shown in FIG. 4.

As shown in FIG. 12, the modulation plate 211 includes an intermediateportion 211 b, and side portions 211 c, 211 c. Light transmission factorof the intermediate portion 211 b is set to zero, and light transmissionfactor of the side portions 211 c, 211 c is set to 1. Accordingly, whenthe modulation plate 211 is directed perpendicular to the collimate beam104, an intermediate portion of the collimate beam 104 is shaded. On theother hand, when the modulation plate 211 is directed parallel to thecollimate beam 104, the collimate beam 104 is not modulated and, passesthrough the modulation plate 211. Thus, it is possible to provide thesame effect as that in the embodiment 1.

A modulation plate 211 shown in FIG. 13 is divided as in the embodiment4 shown in FIG. 8, and light transmission factor of the shaded portion211 b is set to zero, and the other portion 211 c is set to 1.Consequently, it is possible to provide the same effect as that in theembodiment 4 by rotating the modulation plate 211.

In modulation means 111 shown in FIG. 14, a modulation plate 212 and amodulation plate 213 are combined at right angle by sharing the rotationaxes 211 a, 211 a. Therefore, two kinds of super-resolution effects, orreduction and extension of a beam diameter can be switched over from oneto another by switching a rotation angle of the modulation means 111such that one of the modulation plates is directed perpendicular to thecollimate beam 104, and the other is disposed parallel thereto.

As set forth above, according to the embodiment 5, it is possible todrive a high recording density medium by a small-diameter condensingspot, and drive a low recording density medium by a normal condensingspot. As a result, both a conventionally standardized medium and a largecapacity medium can be driven by the same optical head. Alternatively,when the low recording density medium is driven, the modulation means111 according to the embodiment 5 is effective in extending a spot in aradial direction of an optical disk to manage a wide-width track pitch.

Embodiment 6

The embodiment 5 has been described with reference to a case where alaser beam is modulated by rotating the modulation plate 211 of themodulation means 111. However, the modulation means 111 may be providedas shown in FIG. 15. As shown in FIG. 15, modulation means 221 isprovided in a hollow cylindrical form, or in a hollow rectangular andcylindrical form. In either case, the modulation means 221 is rotatablysupported at a position to shade a collimate beam 104. FIGS. 16 and 17shown specific patterns of light transmission factor in the modulationmeans.

The modulation means 221 shown in FIG. 16 can provide a super-resolutioncondensing spot depending upon the same principle as that described inthe embodiment 1. That is, when the light transmission factor is set tozero at the shaded portion, and is set to 1 at the other portion, and amodulation plate 222 is directed perpendicular to the collimate beam104, a beam intermediate portion is shaded to provide a condensing spothaving a reduced diameter. Further, when the modulation means 221 isrotated to direct the modulation plate 223 in a direction perpendicularto the collimate beam 104, a peripheral portion of the beam is shaded toprovide a condensing spot having an extended diameter.

In the modulation means 211 shown in FIG. 17, a modulation pattern inprovided on a peripheral surface of a cylinder. It must be noted that ashape of the modulation means 221 should not be limited to theseembodiments.

Embodiment 7

The embodiment 5 has been described with reference to a case where themodulation plate 211 is rotated about the rotation axes 211 a, 211 a.However, in addition to the same function as that in the embodiment 5,another function may be provided to rotate modulation means 231 about anoptical axis of a collimate beam 104 as shown in FIG. 18. In this case,if a transmitted light mutilation pattern in the embodiment 7 is formedas in the transmitted light modulation pattern illustrated in theembodiment 5, it is possible to reduce a condensing spot of a beam inone direction as in the embodiment 5, and rotate the modulation means231 about the optical axis of the collimate beam 104 so as to reduce thecondensing spot in all directions.

By making use of the above fact, it is possible to realize an operationthat a large servo signal is obtained by reducing a condensing spotdiameter in a radial direction of a disk during seek, and a large dataregeneration signal is obtained by reducing the condensing spot diameterin a circumferential direction of the disk during regeneration.

Embodiment 8

In the embodiment 8 shown in FIG. 19, modulation means includes opticalcomponents which are mechanically driven. As shown in FIG. 19, themodulation means of the embodiment 8 includes two modulation plates 241,242. The modulation plates 241, 242 have thicknesses which can beneglected with respect to a beam width, and have a function of rotatingabout axes 241 a, 242 a. In this case, the rotation axes 241 a and 242 aof the modulation plates 241, 242 are supported on both sides of acollimate beam 104 such that edges of the modulation plates 241, 242 areopposed to each other at an intermediate position.

A description will now be given of the operation. First, it is possibleto set a mode to provide the collimate beam 104 with no modulation bydirecting the modulation plates 241 and 242 parallel to the collimatebeam 104. Secondly, it is possible to set a mode to provide thecollimate beam 104 with a first modulation by positioning so as to passthe collimate beam 104 through a half surface of one of the modulationplates 241 and 242. Thirdly, it is possible to set a mode to provide thecollimate beam with second modulation by positioning so as to pass thecollimate beam through another half surface of the other of themodulation plates 241 and 242. In such a way, at least three types ofmodulation modes can be set according to the embodiment 8. The twomodulation plates 241, 242 may be synchronously rotated so as to providea desired condensing spot shape, or may be independently rotated.

Embodiment 9

In the embodiment 9 shown in FIG. 20, modulation means includes opticalcomponents which are mechanically driven. As shown in FIG. 20, themodulation means of the embodiment 9 includes a flat modulation plate251 which moves in a one-dimensional direction or in a two-dimensionaldirection in a plane extending in a direction perpendicular to atravelling direction of a collimate beam 104. That is, modulationpatterns are selected by the plane movement of the modulation plate 251of the embodiment 9. FIGS. 21 and 22 show specific patterns of lighttransmission factor of the modulation plate 251 as examples.

In the embodiment of the modulation plate 251 shown in FIG. 21, aplurality of modulation patterns are arranged in the one-dimensionaldirection, and a modulation pattern to provide a desired condensing spotshape can be selected by movement in the one-dimensional direction. InFIG. 21, patterns as described in the conventional super-resolutiontechnique or the above embodiments are employed as the respectivemodulation patterns. Further, the modulation plate 251 is advantageousin a switching operation of various condensing spot shapes since thenumber of the modulation patterns can be easier increased in theembodiment 9 than would be increased in the embodiments 5 to 8 in viewof a mechanism.

In the embodiment of the modulation plate 251 shown in FIG. 22, aplurality of modulation patterns are arranged in the two-dimensionaldirection, and a modulation pattern to provide a desired condensing spotshape can be selected by movement in the two-dimensional direction. InFIG. 22, as in the modulation plate 251 shown in FIG. 21, patterns asdescribed in the conventional super-resolution technique or the aboveembodiments are employed as the respective modulation patterns. Further,the modulation plate 251 is advantageous in a switching operation ofvarious condensing spot shapes since the number of the modulationpatterns can be easier increased in the embodiment 9 than would beincreased in the embodiments 5 to 8 in view of a mechanism.

Embodiment 10

In the embodiment 10 shown in FIG. 23, optical components are providedto mechanically drive modulation means. In the embodiments 5 to 9, alaser beam is modulated by an amplitude of transmitted light while aphase thereof is modulated in the embodiment 10. Consequently, aconfiguration of the embodiment 10 is identical with those of theembodiments 5 to 9 except for a modulation plate used to spatiallymodulate index of refraction with respect to the transmitted light inthe embodiment 10.

In the embodiments 5 to 9, the amplitude of the transmitted light ismodulated as an example, provided that light transmission factor of ashaded portion is set to zero, and the light transmission factor of theother portion is set to 1. However, as shown in the embodiment 10, thephase of the transmitted light may be modulated by providing adifference between the index of refraction sensed by the transmittedlight at the shaded portion and the index of refraction sensed by thetransmitted light at the other portion. Thereby, it is also possible tocontrol a condensing spot shape as in the embodiments 5 to 9.

In a system of mechanically switching the modulation means as in theembodiments 5 to 10, a mechanism is simple so that design andfabrication thereof is facilitated, and cost may be possibly reduced.

Embodiment 11

Referring now to FIG. 24, modulation means of the embodiment 11 includesoptical components which are electrically driven. As the modulationmeans, there is employed a flat modulation plate 311 including aplurality of segments 313 to 317. In this case, the respective segments313 to 317 of the modulation plate 311 are independently controlled byelectric information from a control circuit 312 which is externallymounted. A collimate beam 104 passes through the modulation plate 311.As is generally known, in the modulation plate (liquid crystal switch)311, it is possible to vary a light transmission amount by voltageapplied to a control electrode. Therefore, the respective segments 313to 317 can modulate an amount of transmitted light of the collimate beam104 passing through the respective segments. As a result, the modulationplate 311 can provide an intensity distribution of a transmitted beamwith space modulation.

FIGS. 25(a) to 25(d) show specific embodiments of dividing patterns inthe segments of the modulation plate 311. As described above, themodulation plate 311 is divided into five segments 313 to 317 so thatthe segment 313 is disposed at an intermediate portion of the collimatebeam 104, and the segments 314 to 317 are disposed at peripheral portionthereof. In FIGS. 25(a) to 25(d), four types of modulation patterns areillustrated. In the drawings, the shaded portion is set to shade thebeam, and the other portion is set to pass the beam. Thereby, it ispossible to provide a reduced condensing spot in FIG. 25(a), and providean extended condensing spot in FIG. 25(b). Further, it is possible toprovide a vertically elongated condensing spot in FIG. 25(c), andprovide a transversely elongated condensing spot in FIG. 25(d).

It must be noted that the dividing patterns in the segments of themodulation plate 311 should not be limited to this case, and may bedesigned so as to provide a desired condensing spot shape. In addition,in the operation of the modulation plate 311, a switching speed isfaster than that in the mechanical means as described above. As aresult, a high speed response can be realized.

Embodiment 12

Though the amount of transmitted light of the laser beam is modulated bythe modulation plate 311 in the embodiment 11, in the embodiment 12, aphase of the laser beam is modulated. That is, modulation means of theembodiment 12 is provided with a flat phase modulator including aplurality of segments 323 to 327. The phase modulator 321 includes anelectro-optical crystal plate such as LiNbo₃, and a plurality pairs ofparallel flat electrodes. The respective pairs of electrodes areindependently controlled by electric information from a control circuit322 which is externally mounted. A collimate beam 104 passes through themodulation plate 321. As is generally known, in the electro-opticalcrystal plate, index of refraction can be varied by an electric fieldapplied to crystal. Therefore, the respective pairs of electrodes canprovide a difference between indexes of refraction of a transmitted beamat an occupied portion so as to modulate the phase of the beam. As aresult, in the entire modulation plate 321, it is possible to provide aphase distribution of the transmitted beam with space modulation.

In order to specifically illustrate dividing patterns in the segments323 to 327, FIGS. 27(a) to 27(d) show four types of modulation patterns.The modulation plate 321 is controlled such that a desired phasedifference occurs between the transmitted light at the shaded portion inthe drawings and the transmitted light at the other portion. Thereby, itis possible to provide a reduced condensing spot in FIG. 27(a), andprovide an extended condensing spot in FIG. 27(b). Further, it ispossible to provide a vertically elongated condensing spot in FIG.27(c), and provide a transversely elongated condensing spot in FIG.27(d).

Embodiment 13

FIG. 28 shows phase modulation means which is provided with a bulk-likephase modulator 331 including a plurality of segments 333 to 335. Thephase modulator 331 includes an electro-optical crystal plate such asKDP, and a pair of parallel flat electrodes. The pair of electrodes areindependently controlled by electric information from an externalcontrol circuit 332. A collimate beam 104 passes through the modulator331.

Specifically, the segments 333 to 334 are divided into, for example,three segments as shown in FIG. 29. There is provided a differencebetween indexes of refraction by applying voltage V and inverse voltageV to the intermediate segment 333, and the two outer segments 334,respectively. Thereby, the phase can be modulated by the difference inthe index of refraction with respect to the collimate beam 104 passingthrough the segments 333 to 334. Further, space modulation is providedto a phase distribution of the transmitted beam on an emission surfaceof the phase modulation means. It is thereby possible to control acondensing spot shape depending upon the same operation principle asthat in the embodiment 3.

Alternatively, the phase modulation means may include the intermediatesegment 333, exclusively. In this case, air having index of refractionof 1 serves as the outer segments 334, 334.

In a system of switching by electric means as described in theembodiments 11 to 13, a switching speed is typically faster than that inthe mechanical means as described in the embodiments 5 to 10. As aresult, a high speed response can be possibly realized. Additionally,the system requires no movable portion so that high reliability can beexpected.

Embodiment 14

A description will now be given of a condensing spot switching method inan optical disk unit which is equipped with a beam condensing apparatusdescribed in the embodiments 1 to 13. An optical disk in accordance withthe ISO standard, which has been put to practical use, has a track pitchof 1.6 μm as set forth above. Another optical disk which has beenstudied according to the next generation ISO standard, has a track pitchin a range of 1.3 to 1.4 μm. Further, other optical disks having thetrack pitches of 1.2, 1.0, or 0.8 μm will be developed in the future.

FIG. 30 shows algorithm in case the optical disks having the differenttrack pitches as described above are driven by the same optical diskunit. First, the optical disk is mounted on the optical disk unit, andthe optical disk is activated (in Step 399). Subsequently, the diskrevolution is stabilized (in Step 400), and a laser is turned ON (inStep 401). Next, a focus servo is pulled in (in Step 402), and aftercompletion of the focus pulling in, control track information in PEP isread at a control track PEP area (in Step 403). The control trackinformation includes information relevant to the track pitch.

Further, a condensing spot diameter is switched over depending upon aread value of the track pitch. Thereby, the optical disk unit is set tomanage the condensing spot diameter which is adaptable to the trackpitch (in Step 404). Subsequently, a tracking servo is pulled in as inthe prior art (in Step 405), and a recordable and regenerable state isestablished (in Step 406).

A description will now be given of a mode setting method of thecondensing spot diameter in case the modulation means of the embodiment4 shown in FIG. 8 is employed in the optical disk unit with reference toFIG. 31. First, if it is found that the driven disk has the track pitchof 1.0 μm depending upon the PEP information, an intermediate portion ofa collimate beam is shaded by the modulation means 111 to reduce thecondensing spot diameter. Alternatively, if the driven disk has thetrack pitch of 1.6 μm, a peripheral portion of the collimate beam isshaded by the modulation means 111 to extend the condensing spotdiameter. Further, if the driven disk has the track pitch of 1.2 μm, thecollimate beam is not shaded by the modulation means 111 to provide thecondensing spot diameter as in the prior art.

In the method as described above, the optical disks having various typesof track pitches can be driven by only one optical disk unit byswitching the condensing spot diameter according to the track pitches.As a result, it is possible to ensure compatibility to the optical disksbased upon the different standards with sufficient performance andreliability.

Embodiment 15

FIG. 32 shows algorithm illustrating a condensing spot switching methodaccording to the embodiment 15. In the embodiment 15, the operationproceeds, as in the embodiment 14, from Step 399 where an optical diskis activated to Step 404 where a condensing spot diameter is switchedover to an appropriate condensing spot diameter according to a trackpitch. However, in the embodiment 15, the operation proceeds from Step404 to Step 410 where an amplitude of a tracking servo sensor signal ismonitored by a monitor circuit 421 (see FIG. 33), and a modulationamount in modulation means 111 is adjusted so as to maximize theamplitude.

FIG. 33 shows the above-mentioned monitor circuit 421 for the amplitudeof the sensor signal. An optical disk unit is set to have the optimalcondensing spot diameter for tracking by automatically adjusting toprovide the optimal tracking servo signal in Step 410, and thereafterthe optical disk unit conventionally pulls in a tracking servo in Step405, and is in a recordable and regenerable state (in Step 406). In thiscase, it is also possible to monitor a track crossing signal, a discretesensor signal, or a tracking error signal obtained by a differencebetween the sensor signals instead of monitoring the tracking servosignal.

By the process described in embodiment 15, it is possible to absorbvariation in a tracking servo signal characteristic which is differentfor each combination of an optical disk medium and the optical diskunit, and to extend a servo stability margin. Further, optimization ofthe tracking error signal waveform is effective in prevention ofcounting error during a seek operation of a track, and results inrealizing reduction of a mean seek time and improvement of seekreliability.

Embodiment 16

FIG. 34 shows algorithm illustrating a condensing spot switching methodaccording to the embodiment 16. In the embodiment 16, the operationproceeds, as in the above embodiment, from Step 399 where an opticaldisk is activated to Step 405 where a tracking servo is pulled in.However, in the embodiment 16, the operation proceeds from Step 405 toStep 411 where an amplitude of a regenerative signal of an emboss signalis monitored by a monitor circuit 431 (see FIG. 35), and a modulationamount in modulation means 111 is adjusted so as to maximize theamplitude of the regenerative signal at the maximum frequency. FIG. 35shows the above-mentioned monitor circuit 431 for the amplitude of theregenerative signal. An optical disk unit is set to have the optimalcondensing spot diameter for data regeneration by automatic adjustmentto optimize the regenerative signal in Step 411, and thereafter theoptical disk unit is in a recordable and regenerable state as in theprior art in Step 406.

Here, in case the modulation means as described in the embodiment 11 isemployed, it is possible to independently adjust the amplitudes of thetracking servo signal and the regenerative signal when a condensing spotshape is adjusted by the modulation means. By the process described inembodiment 16, it is possible to absorb variation in a data regenerationsignal characteristic which is different for each combination of anoptical disk medium and the optical disk unit, and to extend aregenerative signal detection margin. As a result, it is possible toimprove reading accuracy of a signal with respect to the optical disksin accordance with many generations standards, and various types ofstandards, and to realize the data regeneration with higher reliabilityand a smaller number of error.

Embodiment 17

The embodiments 14 to 16 have been described with reference to a casewhere the condensing spot is switched depending upon the control trackinformation. In addition to the case, it is also possible to improve aperformance of an optical disk unit by switching the condensing spotaccording to an operation mode of an optical disk unit.

FIG. 36 shows relations between a shape of a condensing spot 511 and adimension of a track 512 corresponding to each optical disk operationmode. At a time of seek, a modulation amount of modulation means 111 isset so as to provide a condensing spot width which can provide theoptimal tracking servo signal for the seek, i.e., a track crossingsignal by, for example, a method as described in the embodiment 15.Further, at a time of regeneration, the modulation amount of themodulation means 111 is set so as to provide a condensing spot lengthand a condensing spot width which can provide the optimal regenerativesignal by, for example, a method as described in the embodiment 16.

At a time of recording, the spot diameter is not restricted. In a systemto modulate an amplitude of a collimate beam by the modulation means111, there is great loss of laser power as set forth above. On the otherhand, in an optical disk unit, the upper bound of a data transfer rate(i.e., disk revolution) is restricted due to limit of the maximum outputpower of a semiconductor laser, or the upper bound of recording powerwhich is available in a recording medium is restricted. Thus, the lossof the laser power is a major issue in view of a performance. Hence, itis preferable that the optical disk is driven without the amplitudemodulation at the time of recording or erasing. Meanwhile, a recordingcan be performed even if the condensing spot diameter at the time ofrecording is not reduced to an extent of reduction at the time ofregeneration. The method described in the embodiment 17 enables anoperation that no amplitude modulation is provided at the time ofrecording while the condensing spot diameter is reduced at the time ofregeneration.

At the time of erasing, the condensing spot width is extended so as tocover a full recording track width in which a recording mark exists.

According to the embodiment 17 using the method as described above, itis possible to improve reading accuracy of a signal with respect to theoptical disks having different recording densities and track pitches inaccordance with many generations standards, and various types ofstandards so as to realize the data regeneration with higher reliabilityand a smaller number of error. Further, highly reliable data recordingcan be realized with no crosstalk because erroneously unerased data isprevented from being left. In addition, according to the embodiment 17,a super-resolution technique can be used to regenerate a high densityrecording data, and high recording power can be also provided. It isthereby possible to further improve compatibility for various types ofoptical disks in accordance with different standards.

Embodiment 18

The embodiment 18 is identical with the embodiment 17 in that acondensing spot switching function is applied to improve a performance.However, the embodiment 18 is different from the embodiment 17 in thatan additional method is employed in the embodiment 18 to vary acondensing spot shape when retry process is executed to reread a sectorin which regeneration becomes impossible due to many errors at a time ofdata regeneration.

FIG. 37 shows algorithm according to the embodiment 18. According to thealgorithm in FIG. 37, sector read is executed in Step 415, and if it isdecided that the sector read is not normal in Step 416, the condensingspot shape is modified in Step 417 and the sector read is executed inStep 415 again. As set forth above, in the embodiment 18, a modulationsignal set to provide the condensing spot to be optimal is varied in apredetermined range so as to perform retry regeneration. It is therebypossible to increase possibility that a condition incapable of readingthe signal can be avoided, and improve reliability of data retention.

Embodiment 19

FIG. 39 shows shapes of recording bits 531 in the control track PEP areaas described in the embodiment 14, a condensing spot 511 scanning on therecording bit, and a regenerative signal waveform at this time.

Information is recorded in very low density, and is encoded in a systemin which one area having the recording bits 531 and the other areahaving no recording bit are alternated at a very long interval. Therecording bit 531 has a diameter of 0.4 μm, and is regularly disposed ona period of about 0.8 μm. There has been no problem since regenerationin the prior art is performed by a condensing spot having a largerdiameter than that of the recording bit 531. However, in case thecondensing spot 511 is reduced, there is a problem in that noregenerative signal can be obtained, and erroneous regeneration dataoccurs when the condensing spot 511 passes just between recording bitsequences even if the area having the recording bit is regenerated.

Hence, in the embodiment 19, the condensing spot diameter is extended ata time of PEP area regeneration in Step 418 as shown in the algorithm ofFIG. 38. As a result, it is possible to improve reading accuracy of thecontrol track PEP area with respect to any type of optical disk, and toreduce a mean drive starting time. The PEP area accommodates the mostbasic parameter, and is first read at a time of activating the disk.There is a great effect of improvement of reliability of the read.

Embodiment 20

In the embodiment 20, a condensing spot diameter is extended in bothvertical and lateral directions so as to equivalently reduce numericalaperture NA of an objective lens 105 (see FIG. 4) as the condenser. Asis generally known, in a condensing system employing a lens, as thenumerical aperture NA becomes larger, a depth of focus becomesshallower.

Typically, in a focus control system of an optical disk unit, as thenumerical aperture NA becomes larger and the depth of focus becomesshallower, a follow-up capability of a focus servo is more reduced dueto surface fluttering of the disk and inclination of a disk surface. Inparticular, the focus control system is easily affected by externaldisturbance such as surface fluttering so that a focus pulling infailure easily occurs. The failure leads a retry operation, resulting ina longer activating time.

Hence, in the embodiment 20, as shown in the algorithm in FIG. 40, thecondensing spot diameter is extended in both the vertical and lateraldirections (in Step 419) before starting to pull in the focus (in Step402), and in this condition, the focus pulling in is completed.According to later Steps as described in the embodiments 14 to 16, thecondensing spot is set (in Step 420). As a result, it is possible toimprove stability of the focus pulling in, and reduce a means drivestarting time. Further, it is possible to extend a focus pulling inrange with respect to any type of optical disk so that a disk receivingrange can be extended, and compatibility and versatility can be alsoimproved.

As set forth above, according to the first aspect of the presentinvention, it is possible to use the small-diameter condensing spot withrespect to the high recording density medium, and use the large-diametercondensing spot with respect to the low recording density medium. As aresult, there is an effect in that various types of optical recordingmedia having different recording capacity can be managed by the sameoptical head.

According to the second aspect of the present invention, the light beamcondensing apparatus is provided with the control means for controllingthe modulation means. As a result, there is an effect in that it ispossible to control the modulation means in response to a signal fromthe control means.

According to the third aspect of the present invention, the transmissionfactor of the collimate beam is varied so as to vary the shape of thecondensing spot. As a result, as in the first aspect, there is an effectin that various types of optical recording media having differentrecording capacity can be managed by the same optical head.

According to the fourth aspect of the present invention, the phase ofthe collimate beam is varied so as to vary the shape of the condensingspot. Therefore, it is possible to reduce and extend the diameter of thecondensing spot without shading the collimate beam. As a result, thereis an effect in that the loss of power due to the shading can beavoided.

According to the fifth aspect of the present invention, the shape of thecondensing spot can be switched over by simply rotating the flatmodulation means. As a result, there is an effect in that the light beamapparatus can have a simpler configuration.

According to the sixth aspect of the present invention, the flatmodulation means is provided rotatably about the optical axis so thatthe condensing spot can be reduced in all directions. As a result, thereis an effect in that the large servo signal can be obtained by reducingthe condensing spot diameter in the radial direction of the opticalrecording medium during the seek, and the large information regenerationsignal can be obtained by reducing the condensing spot diameter in thecircumferential direction of the optical recording medium during theregeneration.

According to the seventh aspect of the present invention, the two kindsof condensing spot diameters can be switched over from one to another.As a result, there is an effect in that the small-diameter condensingspot can be used for the high recording density medium, and thewide-width track pitch of the low recording density medium can bemanaged by extending the condensing spot in the radial direction of theoptical recording medium.

According to the eighth aspect of the present invention, it is possibleto form the plurality of modulation patterns on the peripheral surfaceof the cylindrical body which is rotatably supported. As a result, thereis an effect in that different types of the shapes of the condensingspot can be provided.

According to the ninth aspect of the present invention, it is possibleto set the mode to provide the collimate beam with no modulation, themode to provide the first modulation, and the mode to provide the secondmodulation. As a result, there is an effect in that the three kinds ofmodulation modes can be optionally selected.

According to the tenth aspect of the present invention, it is possibleto easily increase the number of the modulation patterns. As a result,there is an effect in that multi-stage switching can be performed in theshape of the condensing spot.

According to the eleventh aspect of the present invention, it ispossible to electrically vary the modulation pattern so as to acceleratethe switching speed. As a result, there is an effect in that the highspeed response can be realized.

According to the twelfth aspect of the present invention, the modulationpattern of the modulation means is formed by the rectangular modulationsection which is positioned at the intermediate portion of the collimatebeam, and has the longitudinal side longer than the collimate beamdiameter. As a result, there is an effect in that it is possible toreduce or extend the diameter of the condensing spot in one direction.

According to the thirteenth aspect of the present invention, themodulation pattern of modulation means is formed by the circularmodulation section which is positioned coaxially with the collimatebeam, and has the diameter smaller than the collimate beam diameter. Asa result, there is an effect in that it is possible to reduce or extendthe diameter of the condensing spot in all directions.

According to the fourteenth aspect of the present invention, thecondensing spot can be switched over according to the track pitch of theoptical recording medium. Thus, the optical recording media havingvarious types of track pitches can be driven by only one drive unit. Asa result, there is an effect in that it is possible to ensurecompatibility to the optical recording media in accordance with thedifferent standards with sufficient performance and reliability.

According to the fifteenth aspect of the present invention, it ispossible to absorb the variation in the tracking servo signal which isdifferent for each combination of the optical recording medium and adrive unit thereof. As a result, there is an effect in that margin ofthe servo stability can be extended.

According to the sixteenth aspect of the present invention, it ispossible to absorb the variation in the information regeneration signalcharacteristic which is different for each combination of the opticalrecording medium and a drive unit thereof. As a result, there is aneffect in that the signal reading accuracy can be improved with respectto the optical recording media in accordance with various standards soas to realize highly reliable information regeneration with a smallernumber of error.

According to the seventeenth aspect of the present invention, it ispossible to improve reading accuracy of the track pitch information inthe control track area with respect to various types of opticalrecording media. As a result, there is an effect in that the mean drivestarting time can be reduced.

According to the eighteenth aspect of the present invention, it ispossible to improve the stability of the focus pulling in so that themean drive starting time can be reduced. Further, the focus pulling inrange can be extended. As a result, there is an effect in that thereceiving range of the optical recording medium can be extended, andcompatibility and versatility can be also improved.

According to the nineteenth aspect of the present invention, it ispossible to provide the amplitude modulation to the collimated beam atthe time of seek and regeneration, and provide no amplitude modulationto the collimated beam at the time of recording so that the loss oflaser beam at the time of recording can be avoided. As a result, thereis an effect in that it is possible to use the super-resolutiontechnique to regenerate the high density recording information, andprovide the high laser power of condensed spot to record information.

According to the twentieth aspect of the present invention, it ispossible to improve possibility that the condition incapable of readingthe signal can be avoided. As a result, there is an effect in thatreliability of information retention can be improved.

While preferred embodiments of the invention have been described usingspecific terms, such description is for illustrative purposes only, andit is to be understood that changes and variations may be made withoutdeparting from the spirit or scope of the following claims.

What is claimed is:
 1. A method of driving an optical recording mediumby applying a light beam condensing apparatus, the method comprising:emitting a laser beam from a laser oscillator; reading track pitchinformation in a control track area by a condensing beam emitted fromsaid light beam condensing apparatus, transforming said emitted laserbeam into a collimate beam, and condensing and introducing saidcollimate beam into said control track area of the optical recordingmedium; modulating said collimate beam by controlling modulation meansof said light beam condensing apparatus depending upon said read trackpitch information; setting a condensing spot shape of said condensingbeam introduced into said control track area of said optical recordingmedium to be adaptable to said track pitch; detecting an amplitude of atracking servo sensor signal at a time of said setting of the shape ofsaid condensing spot; adjusting said shape of said condensing spot bycontrolling said modulation means so as to maximize said detectedamplitude; and performing recording and regeneration of said opticalrecording medium at said adjusted condensing spot.
 2. The methodaccording to claim 1, further comprising: detecting an amplitude of aregenerative signal of an emboss signal prior to performing regenerationof said optical recording medium at said condensing spot; and adjustingto provide an optimal condensing spot shape for information regenerationby controlling said modulation means so as to maximize said detectedamplitude.
 3. The method according to claim 1, further comprising:setting said condensing spot shape to have a large diameter bycontrolling said modulation means of said light beam condensingapparatus prior to reading said track pitch information in said controltrack area.
 4. The method according to claim 1, further comprising:setting said condensing spot shape to be large by controlling saidmodulation means of said light beam condensing apparatus prior to focuspulling in for reading said track pitch information in said controltrack area.